How to evaluate a silicon controlled rectifier's quality
There are two types of thyristors: one-way thyristor and two-way thyristor, both of which have three electrodes. A one-way thyristor has a cathode (K), an anode (A), and a control electrode (G). The bidirectional thyristor is equivalent to two single thyristors connected in reverse parallel. That is, one of the unidirectional silicon anodes is connected to the other cathode, and its leading end is called T2 pole, and one of the unidirectional silicon cathodes is connected to the other anode, and its leading end is called T2 pole, and the rest are control poles. Pole (G).
1. Discrimination of unidirectional and bidirectional thyristors: First, measure the two poles randomly. If the positive and negative measurement pointers do not move (R×1 block), it may be A, K or G, A poles (for unidirectional thyristors) ) It may also be T2, T1 or T2, G pole (for triac). If one of the measurements indicates tens to hundreds of ohms, it must be a one-way thyristor. And the red pen is connected to the K pole, the black pen is connected to the G pole, and the rest is the A pole. If the positive and negative test indications are tens to hundreds of ohms, it must be a triac. Then turn the knob to R×1 or R×10 for retesting, there must be one with a slightly larger resistance value, then the red pen connected to the slightly larger one is the G pole, the black pen is connected to the T1 pole, and the rest are T2 poles .
2. The difference in performance: Turn the knob to R×1 gear, for 1~6A unidirectional thyristor, the red pen is connected to the K pole, and the black pen is connected to the G and A poles at the same time, and the black pen is not separated from the A pole. Disconnect the G pole, and the pointer should indicate tens of ohms to one hundred ohms. At this time, the thyristor has been triggered, and the trigger voltage is low (or the trigger current is small). Then turn off the A pole momentarily and turn it on again, the pointer should return to the ∞ position, indicating that the SCR is good.
For 1~6A bidirectional thyristor, the red pen is connected to the T1 pole, and the black pen is connected to the G and T2 poles at the same time. The G pole should be disconnected under the premise of ensuring that the black pen does not separate from the T2 pole. The pointer should indicate tens to more than one hundred Europe (depending on the size of the thyristor current and different manufacturers). Then reverse the two pens, repeat the above steps to measure once, and the pointer indication is more than ten to tens of ohms larger than the previous one, indicating that the SCR is good, and the trigger voltage (or current) is small. If the G pole is turned off while the A pole or T2 pole is kept connected, the pointer immediately returns to the ∞ position, indicating that the trigger current of the thyristor is too large or damaged. It can be further measured according to the method in Figure 2. For the one-way thyristor, the light should be on when the switch K is closed, and the light should not go out when the K switch is turned off, otherwise the thyristor is damaged.
For bidirectional thyristor, close the switch K, the light should be on, turn off K, the light should not go out. Then reverse the battery, repeat the above steps, should be the same result, it is good. Otherwise, the device is damaged.
